Nitride semiconductors are being paid attention to and are being actively studied and developed as semiconductor materials capable of comprising blue light-emitting elements (LEDs, LDs) or pure green light-emitting elements. While among elements employing such nitride semiconductors, blue LEDs or pure green LEDs of high luminance are being put to use as light sources such as full-colored LED displays, traffic lights or light sources in image scanners, it is expected that such LEDs are being employed for an even wider variety of uses in the future. Such LED elements are basically arranged in that there are sequentially laminated, on to a sapphire substrate, a buffer layer consisting of GaN, an n-sided contact layer consisting of Si-doped GaN, an active layer of InGaN of single-quantum-well structure (SQW) or of multi-quantum-well structure containing InGaN, a p-sided cladding layer consisting of Mg-doped AlGaN, and a p-sided contact layer consisting of Mg-doped GaN in this order, and the LED elements exhibit extremely superior characteristics in which a blue LED with an emission wavelength of 450 nm at 20 mA exhibits 5 mW and an external quantum efficiency of 9.1% while a green LED of 520 nm exhibits 3 mW and an external quantum efficiency of 6.3%.
However, accompanying the spread of use of such nitride semiconductors in the future, it is expected that demands for reductions of leakage currents and improvements in ESD(Electrostatic discharge) tolerance will increase in addition to emission intensities and luminous efficiencies.